1. Field of the Invention
The present invention relates to an improvement in a mounting package for semiconductor devices used in microwave, X or Ku bands.
2. Description of Related Art
In semiconductor mounting packages for mounting high-frequency devices used in microwave, X and Ku bands, there is a demand for miniaturization, cost-reduction and improvement in performance. For example, a four-pin resin package structure as shown in FIGS. 7A and 7B is known as a package for mounting a HEMT (High Electron Mobility Transistor) device for a low-noise amplifier used in a 12 GHz band receiver system (see JP 9(1997)-213826 A, for example).
FIG. 7A is a plan view of a semiconductor device, and FIG. 7B is a sectional view thereof. A premold resin 1 is formed with a source lead 2, a gate lead 3 and a drain lead 4 embedded as one piece. The source lead 2 has a die pad portion 2a and an internal terminal portion 2b that are located inside a recessed portion 7 of the premold resin 1, and an external terminal portion 2c that is located outside the premold resin 1. An HEMT chip 5 is joined to the die pad portion 2a with an electrically conductive adhesive 10. The gate lead 3 and the drain lead 4 extend in a direction perpendicular to the source lead 2, and their internal ends are adjacent to the HEMT chip 5. The source lead 2, the gate lead 3 and the drain lead 4 are molded together with the premold resin 1 in the form of lead frame. After molding, they are separated from the frame (not shown).
The source lead 2 is connected electrically to a source (not shown) of the HEMT chip 5 by bonding wires 6a. A gate (not shown) of the HEMT chip 5 is connected electrically to the gate lead 3 by a bonding wire 6b, and a drain (not shown) thereof is electrically connected to the drain lead 4 by a bonding wire 6c. As shown in FIG. 7B, a cap 9 is attached to an upper end surface of a side wall of the premold resin 1 with an adhesive 8, thus sealing the recessed portion 7.
FIGS. 8A and 8B show a structure of where the HEMT chip 5 and the bonding wires 6a to 6c are connected in the above-described semiconductor device. FIG. 8A is a plan view, and FIG. 8B is a sectional view. The bonding wires 6a to 6c respectively are connected with a source electrode wiring 11, a gate electrode wiring 12 and a drain electrode wiring 13 that are formed on an upper surface of the HEMT chip 5.
FIGS. 9A and 9B respectively show a circuit diagram and a Smith chart of the semiconductor device obtained by mounting the HEMT device on the four-pin resin package in the above-described conventional example in FIG. 9A, numeral 11a denotes a source, numeral 12a denotes a gate, and numeral 13a denotes a drain. The Smith chart in FIG. 9B shows complex impedance (R+j×X). The horizontal line indicates pure resistance (R; inside the circle corresponds to R>0). The top half indicates an inductive reactance component (X>0), while the bottom half indicates a capacitive reactance component (X<0). The left end corresponds to 0 Ω (short circuit), the right end corresponds to ∞Ω (open circuit), and the center corresponds to 50 Ω.
A source inductor 14 shown in FIG. 9A corresponds to an inductance component of the bonding wire 6a as well as a portion of the source lead 2 from the connection position with the bonding wire 6a to an outer end of the external terminal portion 2c in the structure of FIGS. 7A and 7B. As described above, an inductance element is constituted using the bonding wires 6a in the conventional example. In this manner, Gopt (optimum gain matched impedance) and Γopt (minimum noise matched impedance) are adjusted. More specifically, as shown in FIG. 9B, Gopt (optimum gain matched impedance) and Γopt (minimum noise matched impedance) are brought closer to each other, and then matched to the vicinity of 50 Ω.
As described above, in the four-pin resin package in the conventional example, the bonding wires 6a are used as the source inductor 14. Therefore, a variation in the length of the bonding wires 6a at the time of mounting brings about variation in Gopt (optimum gain matched impedance) and Γopt (minimum noise matched impedance) of the HEMT device in microwave, X and Ku bands including the 12 GHz band, as illustrated in FIG. 9B. As a result, high-frequency characteristics, in particular characteristics of gain and noise, vary considerably, thus deteriorating performance stability, causing a problem that a decrease in yield leads to a cost increase.